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Full text of "Text Book Of Mechanical Engineering"

11S                            Forging Cranks.

and          as the            boss.    Heating to a good white heat, it is

put           the hammer, where the ferrule B stamps out the shape of

the             It is next drawn out by suitable tools, called sets, at

top and          (see c and B) until it is of correct length to form the

which is first set down to the proper thickness, and

by means of a ferrule, as before.    The forging is

now of the form E, and all that is necessary is to finish by cutting

corners round the bosses, which will require another

heat—the third ; the first having been used for the large boss and

the setting down, and the second for the small boss,

A Bell Crank Lever, whether large or small, can be made

in a similar manner to the foregoing.    A, Fig. 118, is the finished

lever,   A bar Is taken, as before, of the thickness and width of

the boss.    It is first bent to a right angle—if a small lever this

be done on the anvil beak, but, if large, blocks would be put

the steam hammer, with the hot bar between, as at B.   That

the boss is next formed by ferrule, as at c.   Another heat

will now be found necessary for each arm, in order to set down, as

at p D, to proper section, and the ends are finally cut to curve by

of a chisel or cutter (see Pig. 1.19*2:).

Figs 119 and uga represent the forging of a Small Crank
Shaft, say two inches in diameter, such as can be worked by the
with the aid of a small steam hammer.   A is the finished
and has two crank arms forged upon it at right angles to
other, in the manner of locomotive  axles  for   'inside'
cylinders.   We mast, to begin with, have a slab of iron of square
section, sufficiently krge to form the crank web when  drawn
down,   This is seen at B.   It should also be long enough to
complete the whole shaft when drawn down and swaged in the
manner to be described    The bar B is first to be formed into the
shown at c, by heating to a good white heat and setting
down under the hammer, as at D.   TMs will leave the slab of the
section as the crank web, and, if carefully set down to the
Indicated, the webs will now be in correct position, namely,
at ijgbt angles to each other.   Of course some care must be
the right angle being tested, with a square, and the part
m £ la jttzticalar should be made of such a length that when
* .to:therotind -section it will measure-the correct distance